Cardiff Bay is the area of water created by the Cardiff Barrage in south Cardiff, the capital of Wales. It is also the name commonly given to the areas of the city surrounding the Bay. The creation of Cardiff Bay is now widely regarded as one of the most successful regeneration projects in the United Kingdom. The Bay is supplied by two rivers (Taff and Ely) to form a 500-acre freshwater lake around the former dockland area south of the city centre. The Bay was formerly tidal, with access to the sea limited to a couple of hours each side of high water but now provides 24-hour access through three locks.

Cardiff Bay played a major part in Cardiff's development by being the means of exporting coal from the South Wales Valleys to the rest of the world, helping to power the industrial age.